The present invention relates in general to a device for controlling the supply of air and recycled exhaust gas components into combustion spaces of a self-igniting internal combustion engine and also relates to a method of controlling the supply of such gas components.
In prior art devices of this kind, known for example from U.S. Pat. No. 4,177,777, air sucked in by the engine is metered by an air flow sensor and a control signal indicative of the intake air flow and if desired of other operational parameters of the engine, changes control pressure in a pneumatically operated valve in a return conduit for exhaust gas, thus controlling the quantity of returned exhaust gas components.
In another prior art controlling device of this kind known from U.S. Pat. No. 4,467,775 the control of the amount of the returned exhaust gas is effected according to the deviation of the actual value of the supplied air quantity from a desired air flow value which is determined from operational variables of the engine, particularly from the load. The correction of the actual air flow occurs by changing the quantity of the returned exhaust gas at free suction of air by the engine. The actuation of a control member for the returned exhaust gas is made by means of a pneumatic pressure medium supplied through a pressure transforming device in a control pressure chamber of a setting motor. The pressure transformer in this known controlling device consists of two solenoid controlled 2/2 directional control valves which selectively connect the control pressure space of the setting motor either with outer atmosphere acting as a reference pressure source or with a source of vacuum or low pressure. The actuation of the solenoids of the directional control valve can be made either by an analog or a digitial signal.
This known controlling device adjusts accurately only the quantity of the fed back exhaust gas so as to achieve an optimum combustion at a high rate of exhaust gas recycling, and to reduce emission of NO.sub.x pollutants. At a given engine load or quantity of supplied fuel, the fuel-air ratio is accurately preserved through the control of the fresh air flow by means of the returned exhaust gas control and consequently the proportion of HC and CO pollutants as well as soot or carbon deposit in exhaust gas is kept low.
In the case of self-igniting internal combustion engines however such prior art controlling devices do not meet all operational requirements. In particular, when no special measures are taken, a self-igniting internal combustion engine produces an increased quantity of soot in exhaust gas and care mus be taken that the excessive soot does not reach free atmosphere.